Global wind shifts ended last Ice Age?
Washington: Scientists have claimed that global wind shifts may have ushered in a warmer climate and the birth of human civilisation at the end of the last Ice Age about 20,000 years ago.
An international team has looked to a global shift in winds and propose a chain of events that began with melting of the large northern hemisphere ice sheets about 20,000 years
ago, the `Science` journal reported.
The melting ice sheets reconfigured the planet`s wind belts, pushing warm air and seawater south, and pulling carbon dioxide from the deep ocean into the atmosphere, allowing the planet to heat even further. Their hypothesis makes use of climate data preserved in cave formations, polar ice cores and deep-sea sediments to describe how Earth finally thawed out.
"Finally, we have a clear picture of the global teleconnections in Earth`s climate system that are active across many time scales.
"These same linkages that brought the earth out of the last ice age are active today, and they will almost certainly play a role in future climate change as well," Bob Anderson at
Columbia University, who led the team.
Earth regularly goes into an ice age every 100,000 years or so, as its orientation toward the sun shifts in what are called Milankovitch cycles.
At the peak of the last ice age, about 20,000 years ago, with New York City and large parts of Europe and Asia buried under thick sheets of ice, Earth`s orbit shifted.
It may sound counterintuitive, but the scientists say freshening of the North Atlantic triggered a series of cold spells in Greenland and northern Europe by shutting down the
Gulf Stream current, which usually carries warm water north from the equator.
By 16,000 years ago, the glaciers had beaten a spectacular retreat. This shift in westerly winds would also amplify the warming in both hemispheres by resetting the
planet`s thermostat, according to the scientists.
The displaced westerlies caused heavy mixing in the Southern Ocean around Antarctica, pumping dissolved carbon dioxide from the water into the air. Ice core records show
that between 18,000 and 11,000 years ago atmospheric carbon dioxide levels rose from 185 parts per million to 265 parts per million.
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